Key to the species of the genus Amphithyrus Claus, 1879

1. Coxa 5 with postero-lateral spinous process............................................. A. bispinosus Claus, 1879

- Coxa 5 normal, without any process....................................................................... 2

2. Body and appendages without cuticular sculpture. Pereopod 6; basis with relatively small, crescent-shaped fissure............................................................................................ A. glaber Spandl, 1924

- Body and appendages with reticulate or striate cuticular sculpture. Pereopod 6; basis with relatively large U-shaped fissure, or if fissure is crescent-shaped, cuticular sculpture is prominent................................................... 3

3. Pereopod 6; basis with relatively small crescent-shaped fissure. Cuticular sculpture extends to uropoda................................................................................................. A. sculpturatus Claus, 1879

- Pereopod 6; basis with relatively large U-shaped fissure. Cuticular sculpture not present on uropoda.................... 4

4. Cuticular sculpture striate. Telson about twice as long as last urosomite, with nipple-like process terminally.................................................................................................. A. similis Claus, 1879

- Cuticular sculpture reticulate. Telson shorter than last urosomite, with rounded distal margin...... A. muratus Volkov, 1982